Light source device, backlight assembly and liquid crystal display device having the same

ABSTRACT

A light source device for preventing a light guide plate from being discolored due to a light supplied by a lamp is disclosed. At least one masking film that is made of a transition metal oxide is disposed in a pathway of the light that is emitted by the lamp and transmitted to a display unit to display images in order to cut off ultraviolet rays having particular wavelengths capable of discoloring the light guide plate. Accordingly, it is possible to prevent the light guide plate, which is made of polyolefin resin composition to make it lightweight, from discoloring in yellow.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a liquid crystal display device,and more particularly to a light source device, a backlight assembly anda liquid crystal display device for preventing a light guide plate frombeing discolored due to light emitted by a lamp.

[0003] 2. Description of the Related Art

[0004] Presently, information processing devices are developed forvarious shapes and functions and higher processing speed. Theinformation processing devices convert various type of information intoelectrical signals. Display devices function as an interface betweenusers and the information processing devices such that the users canidentify the information processed by the information processingdevices.

[0005] Recently, the display device manufacturing industry has beenfocusing on developing smaller and lighter liquid display devices. Theliquid display devices provide richer and fuller colors and higherresolutions as compared with conventional display devices, such as a CRT(Cathode Ray Tube). As the result, the liquid display devices have beengaining its popularity among other display devices, for example,computer monitors, household television sets that are hung on a wall,and the like.

[0006] Generally, to operate a liquid crystal display device, a voltageis applied to the liquid crystal in the predetermined molecule arrays tochange the liquid crystal in the other arrays, which alters the opticalcharacteristics of the liquid crystal, such as a double refractivity, arotatory polarization, a dichroism and a light scattering according tothe molecule arrays of the liquid crystal to emit the light. Therefore,the liquid crystal display device can display the images according tothe changes of the optical characteristics of the liquid crystal cell.

[0007]FIG. 1 is an exploded perspective view showing a liquid crystaldisplay device according to the conventional art schematically, and FIG.2 is a sectional view of showing the constructions of a lamp shown inFIG. 1. FIG. 3 is a graph for showing a discoloration of a light guideplate due to light supplied by the lamp shown in FIG. 1.

[0008] Referring to FIGS. 1 and 2, the liquid crystal display devicecomprises a liquid crystal display module for displaying images whenimage signals are applied thereto and a case (not shown) foraccommodating the liquid crystal display module. The liquid crystaldisplay module includes a display unit having a liquid crystal displaypanel for displaying the images.

[0009] The display unit 200 includes the liquid crystal display panel210, a printed circuit board 220 for transferring data signals, aprinted circuit board 212 for transferring gate signals, a tape carrierpackage 230 for transferring data signals and a tape carrier package 250for transferring gate signals.

[0010] The liquid crystal display panel 210 includes a thin filmtransistor board 212 which is normally a transparent glass on which thethin flhn transistors are formed in a matrix, a color filter board 214having RGB pixels that are formed thereon by a thin film process andpresent predetermined colors while the light passes through the colorfilter board 214, and liquid crystal (not shown).

[0011] When the thin film transistors of the thin film transistor board212 are turned on, electric field is created between the pixelelectrodes of the thin film transistor board 212 and the commonelectrodes of the color filter board 214. The electric field changes theliquid crystal layer's array angle, and changes the lighttransmittivity. As a result, it is possible to gain the desired pixels.

[0012] A driving signal and a timing signal are applied to the gatelines and data lines of the thin film transistor in order to control thearray angle of the liquid crystal and the time of arraying the liquidcrystal in the liquid crystal display panel 210. That is, the printedcircuit boards 220 and 240 generate and apply the gate driving signaland the data signal for driving the liquid crystal display device and aplurality of timing signals for applying the gate driving signal and thedata signal, to the gate lines and the data lines of the liquid crystaldisplay panel 210.

[0013] The backlight assembly 300 is provided under the display unit 200to supply the light to the display unit 200 uniformly. The backlightassembly 300 includes a lamp 310 for generating the light. The lamp 310is protected by a lamp cover 312.

[0014] As shown in FIG. 2, the lamp 310 has a glass tube 301 in whichinert gas is filled up and a hot electrode and a cold electrode 303 and305 to which high voltage electricity and low voltage electricity arerespectively applied are disposed at both ends respectively. Metalelectrodes 303 a and 305 a are mounted at the hot and cold electrodes303 and 305, respectively, in the glass tube. As outer voltagesdischarge electricity between the two electrodes, the inert gas 309 isexcited and ultraviolet rays are generated from the inert gas 309. Someultraviolet rays 311 are conversed into visible rays 313 by thefluorescent material in the glass tube 301 and then supplied to thelight guide plate 320.

[0015] The light guide plate 320 has a size corresponding to that of theliquid crystal panel 210 of the display unit 200, which is disposedunder the liquid crystal panel 210 to guide the light emitted by thelamp 310 toward the display unit 200 by changing a pathway of the light.

[0016] A plurality of optical sheets 330 are provided on the light guideplate 320 to make brightness of the light from the light guide plate 320to the liquid crystal display panel 210 uniformly. In addition, a lightreflecting plate 340 provided under the light guide plate 320 reflectleaking light to the light guide plate 320 so as to improve theefficiency of the light.

[0017] The display unit 200 and the backlight assembly 300 are supportedby means of a mold frame 400 used as a receptacle. The mold frame 400 isprovided with a top chassis 500 for preventing the display unit 200 fromdeparting from the mold frame 400 while the printed circuit boards 220and 240 are bent toward outside of the mold frame 400 and fixed to thebottom surface of the mold frame 400.

[0018] The light guide plate 320 of polymethyl methacrylate(hereinafter, referred to as PMMA) effects the size and the weight ofthe liquid crystal display unit. As the size of the light guide plate320 is directly related to a size of the liquid crystal display panel,however, researches have been continued to produce a liquid crystaldisplay device that is light, thin and small by reducing the weight ofthe light guide plate 320 as much as possible.

[0019] Recently, for an example, a light guide plate which usescycloolefin polymer (hereinafter, referred to as COP) has been developedto reduce the weight thereof. As shown in FIG. 3, however, the COP lightguide plate is susceptible to the ultraviolet rays in the light emittedby the lamp 310 as compared with PMMA light guide plate.

[0020] For an example, when the PMMA light guide plate was aged at anordinary temperature for 3300 hours, the PMMA light guide plate hadchanges ΔX and ΔY in the order of 0.015 on X and Y color coordinates.However, the COP light guide plate had changes ΔX and ΔY in the order of0.025 and 0.032 on X and Y color coordinates. This is caused by arecombination reaction of the polyolefin resin composition to theultraviolet rays, and the light guide plate is subjected todiscoloration into yellow when used for a long period of time.

[0021] Besides, as shown in a graph in FIG. 4, when aged for about 3000hours, a maintenance rate of brightness for the PMMA light guide plateis about 70%, while a maintenance rate of brightness for the COP lightguide plate is about 60%.

[0022] Hence, COP light guide plate has the problems of discolorationand degradation of brightness characteristics as aged.

SUMMARY OF THE INVENTION

[0023] The present invention is directed to solving the aforementionedproblems, and accordingly it is an object of the present invention toprovide a light source device for preventing a light guide plate frombeing discolored due to light supplied from a lamp.

[0024] It is another object of the present invention to provide abacklight assembly having the light source device that prevents a lightguide plate from being discolored due to light supplied from a lamp.

[0025] It is further another object of the present invention to providea liquid crystal display device having the backlight assembly thatprevents light guide plate from being discolored due to light suppliedfrom a lamp.

[0026] In order to achieve the above objects of the present invention, alight source device according to the present invention comprises a glasstube, an electrode, and a masking film. The glass tube is filled up witha gas filler, and includes a mixture layer having a fluorescencematerial therein. The electrode is disposed in the glass tube, andgenerates arc in response to an electric signal applied thereto. Themasking film is coated on the glass tube, and cuts off a part ofultraviolet rays emitted from the glass tube.

[0027] According to another aspect of the present invention, a backlightassembly according to the present invention comprises a light generatingsection which has a glass tube filled up with a gas filler and having amixture layer having fluorescence material therein, for generating lightin response to an electric current applied to an electrode which isdisposed in the glass tube. A light masking film is coated on the lightgenerating section to cut off a part of ultraviolet rays in the light.The light transmitted through the light masking film from the lightgenerating section is guided by means of a light guide section to adisplay unit in order to display images.

[0028] According to yet another aspect of the present invention, aliquid crystal display device according to the present inventioncomprises a lamp unit for generating light in response to an electriccurrent applied to an electrode which is disposed in a glass tube filledup with a glass tube and including a mixture layer having fluorescencematerial therein, a light guiding unit for guiding the light, a displayunit for displaying images in response to the light transmitted from thelight guiding means, a film for cutting off a part of ultraviolet raysemitted by the glass tube, a receiving unit for receiving the lamp unitand the light guiding unit, and a top chassis for adjusting a positionof the display unit and for fixing the display unit to the receivingunit by being assembled to face the receiving unit.

[0029] Preferably, the light masking film is positioned on at least oneof an inner surface of the glass tube between the mixture layer and theglass tube, an outer surface of the glass tube, and a light incidencesurface of the light guiding unit into which the light emitted by thelight generating unit is incident.

[0030] Preferably, the light masking film coated on the glass tube has athickness range of about 0.5 μm to about 1 μm, and comprises oneselected from the group consisting of TiO₂, Y₂O₃ and Ce₂O₅. The lightmasking film cuts off ultraviolet rays having wavelengths of 253 nm, 313nm and 365 nm.

[0031] Preferably, the light guiding unit comprises at least onepolyolefin resin composition. The light guiding unit is formed by mixingthe polyolefin resin with one selected from the group consisting ofTiO₂, Y₂O₃, Ce₂O₅ and SiO₂.

[0032] Preferably, the light guiding unit is formed by mixing thepolyolefin resin with a benzene derivative, especially such that any oneof 2-(e⁻-hydroxy-5-methlyphenol)-benzotriazole and p-phenylene-bis(1,3-benzoxizine)-4-5 NE

[0033] According to the light source device of the present invention, abacklight assembly and a liquid crystal display device, at least onelight masking film that is made of transition metal oxide is disposed ina pathway of the light that is emitted by the lamp and transmitted to adisplay unit to display images in order to cut off ultraviolet rayshaving particular wavelengths capable of discoloring the light guideplate. Accordingly, it is possible to prevent the light guide plate,which is made of polyolefin resin composition to make it lightweight,from discoloring in yellow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The above and other objects and advantages of the presentinvention will become readily apparent by reference to the followingdetailed description when considered in conjunction with theaccompanying drawings wherein:

[0035]FIG. 1 is an exploded perspective view schematically showing aliquid crystal display device according to the conventional art;

[0036]FIG. 2 is a sectional view showing a construction of a lamp shownin FIG. 1;

[0037]FIG. 3 is a graph showing discoloration of a light guide plate ofFIG. 2 due to light emitted from the lamp shown in FIG. 1;

[0038]FIG. 4 is a graph showing maintenance rates of brightness of aPMMA light guide plate and a COP light guide plate shown in FIG. 3.

[0039]FIG. 5 is an exploded perspective view schematically showing aliquid crystal display device according to a preferred embodiment of thepresent invention;

[0040]FIGS. 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 and 20are views of showing examples of the constructions of the lamp in abacklight assembly shown in FIG. 5;

[0041]FIGS. 21 and 22 are graphs showing discoloration states of thelight guide plates of the conventional art and the present inventionshown in FIGS. 6 through 20 in a lapse of the time;

[0042]FIGS. 23 and 24 are views showing another example of theconstructions of the lamp in the backlight assembly shown in FIG. 6; and

[0043]FIG. 25 is a graph showing discoloration states of the light guideplates of the conventional art and the present invention shown in FIG.23 in a lapse of the time.

[0044]FIG. 26 is a graph showing a transmission characteristic ofultraviolet rays in a conventional light guide plate and a light guideplate shown in FIG. 23.

[0045]FIG. 27 is a graph showing maintenance rates of brightness for aCOP light guide plate shown in FIG. 23.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] Hereinafter, the preferred embodiment of the present inventionwill be described in detail with reference to the accompanying drawings.

[0047]FIG. 5 is an exploded perspective view schematically showing aliquid crystal display device according to a preferred embodiment of thepresent invention. FIGS. 6, 7, 8 and 9 are views showing examples of theconstructions of the lamp in a backlight assembly shown in FIG. 5.

[0048] Referring to FIGS. 5 and 6, the liquid crystal display deviceincludes a liquid crystal display module for displaying images when animage signal is applied thereto and a case that has front and rear cases1010 and 1020, for receiving the liquid crystal display module.

[0049] The liquid crystal display module includes a display unit 600having a liquid crystal display panel 610 for displaying the images.

[0050] The display unit 600 includes the liquid crystal display panel612, a source printed circuit board 620 which is located near the datalines, a source tape carrier package 630 which is located near the datalines, a gate printed circuit board 640 which is located near the gatelines, and a gate tape carrier package 650 which is located near thegate lines.

[0051] The liquid crystal display panel 610 comprises a thin filmtransistor board 612, a color filter board 614 and a liquid crystal (notshown).

[0052] The thin film transistor board 612 is a transparent glasssubstrate on which thin film transistors are formed in matrix. A dataline is connected with a source terminal of the thin film transistorsand a gate line is connected with a gate terminal of the thin filmtransistors. Furthermore, pixel electrodes made of Indium Tin Oxide as atransparent and conductive material is formed at a drain terminal of thethin film transistors.

[0053] When electric signals are applied to the data line and the gateline, the electric signals are input into the source terminal and thegate terminal of the respective thin film transistor. As the electricsignals are input into the thin film transistors, the thin filmtransistors are respectively turned-on or turned-off, resulting inoutputting the electric signals that are required to form pixels to thedrain terminals.

[0054] The color filter board 614 is provided to face to the thin filmtransistor board 612. The color filter board 614 has RGB pixels whichare formed by a thin film process to present desired colors during thelight is passing through the color filter board 614. A surface of thecolor filter board 614 is covered with common electrodes made of IndiumTin Oxide.

[0055] When the electric current is applied to the gate and sourceterminals of the transistor on the thin film transistor board 612 toturn on the thin film transistor, an electric field is created betweenthe pixel electrodes and common electrodes of the color filter board.This electric field causes to change an array angle of the liquidcrystal injected between the thin film transistor board 612 and thecolor filter board 614, thereby changing light permeability depending onthe changed array angle so as to gain a desired pixels.

[0056] A driving signal and a timing signal are applied to the gate lineand the data line of the thin film transistor in order to control thearray angle of the liquid crystal and the timing for the liquid crystalbeing arranged in the liquid crystal display panel 610.

[0057] As shown in FIG. 5, the source tape carrier package 620 that isone of flexible circuit boards, is attached to the source portion of theliquid crystal display panel 610 to decide the time for applying a datadriving signal. On the other hand, the gate tape carrier package 640 isattached to the gate portion of the liquid crystal display panel 610 todecide the time for applying a gate driving signal.

[0058] The printed circuit boards 620 and 640 are respectively used forapplying the driving signal to the gate line and the data line,respectively, upon receiving image signals input from outside of theliquid crystal display panel 610. The printed circuit boards 620 and 640make contact with the source tape carrier package 630 for the data lineand the gate tape carrier package 650 for the gate line in the liquidcrystal display panel 610, respectively. A source part is formed on theprinted circuit board 620 in order to receive the image signals from aninformation processing device (not shown) such as a computer, etc. Thesource part also provides a data driving signal to the liquid crystaldisplay panel 610. A gate part is formed on the printed circuit board640 to receive the image signals from the information processing device(not shown). The gate part also provides a gate driving signal to thegate line of the liquid crystal display panel 610.

[0059] The printed circuit boards 620 and 640 generate the gate drivingsignal and the data signal, respectively, for driving the liquid crystaldisplay device and the plural timing signals for applying the gatedriving signal and the data signal in an acceptable time. Thus, the gatedriving signal is applied through the gate tape carrier package 650 tothe gate line of the liquid crystal display panel 610, and the datasignal is applied through the source tape carrier package 630 to thedata line of the liquid crystal display panel 610.

[0060] A backlight assembly 700 is disposed under the display unit 600to uniformly supply the light to the display unit 600. The backlightassembly 700 includes a lamp 710 for generating the light. The lamp 710is covered with a lamp cover 712.

[0061] A light guide plate 720 has a size corresponding to that of theliquid crystal panel 610 of the display unit 600. The light guide plate720 is disposed under the liquid crystal panel 610 to guide the lightgenerated by the lamp 710 to the display unit 600 while changing thepathway of the light. A plurality of optical sheets 730 is disposed onthe light guide plate 720 to achieve uniformity of brightness of thelight that is transmitted from the light guide plate 720 to the liquidcrystal display panel 610. A light reflecting plate 740 is providedunder the light guide plate 720 to reflect the leaking light to thelight guide plate 720, thereby increasing the light efficiency.

[0062] The display unit 600 and the backlight assembly 700 are supportedby a mold frame 800, which is used as a receptacle, as shown in FIG. 5.A chassis 900 is disposed on the display unit 600 to prevent the displayunit 600 from being departed from the mold frame 800 while the printedcircuit boards 620 and 640 are bent to outside of the mold frame 800 andfixed to the bottom surface of the mold frame 800.

[0063]FIGS. 7, 8 and 9 are a perspective view, partly broken away, andsectional views, respectively, showing a construction of the lamp 710shown in FIG. 6.

[0064] As shown in FIGS. 7, 8 and 9, the lamp 710 includes a glass tube701 that is transparent and filled up with inert gas 711. The first andsecond electrodes 707 and 709 are disposed at both ends of the glasstube 701, respectively, to receive electric signals that have highvoltage and low voltage, respectively, supplied from outside.

[0065] The first and second electrodes 707 and 709 are integrated withmetal electrodes 707 a and 709 a, respectively, that are placed in theglass tube 701. The metal electrodes 707 a and 709 a operate in responseto the high and low voltages input applied thereto through the first andsecond electrodes 707 and 709. When the first and second electrodes 707and 709 discharge electric current, the inert gas that fills up theglass tube 701 is excited due to the electric discharge of the metalelectrodes 707 a and 709 a and emit ultraviolet rays.

[0066] On the other hand, a fluorescent layer 705 made of a fluorescentmaterial or a mixture of fluorescent materials is coated on the innersurface of the glass tube 702 to convert a part of the ultraviolet rays713, which is emitted during the electric discharge of the lamp 710,into visual rays 715, thereby generating the light.

[0067] In addition, the masking film 703 is coated on the inner surfaceof the glass tube 701 to be placed between the fluorescent layer 705 andthe inner surface of the glass tube 701, to cut off particularultraviolet rays having certain wavelengths in the ultraviolet rays 713.

[0068] The masking film 703 comprises a transitional metal oxide (e.g.,TiO₂, Y₂O₃ and Ce₂O₅). The masking film 703 can be made of SiO₂. Themasking film 703 is coated on the inner surface of the glass tube 701 bya thickness of 0.5 to 1 μm.

[0069] When electric current is applied from the outside to the firstand second electrodes 707 and 709 and the metal electrodes 707 a and 709a start an operation of the electric discharge, the inert gas 711 isexcited to generate the ultraviolet rays 713. Some of the ultravioletrays 713 is converted into the visual rays 715 by the fluorescent layer705 and then emitted toward the light guide plate 720.

[0070] The ultraviolet rays having wavelengths of 253 nm, 313 nm and 365nm in the rest ultraviolet rays 713 are reflected by the masking film703 and are not emitted out of the glass tube 701. That is, the restultraviolet rays, except for the ultraviolet rays having the wavelengthsof 253 nm, 313 nm and 365 nm, and the visual rays having wavelengths of380 nm to 700 nm are supplied through the glass tube 701 to the lightguide plate 720.

[0071] Referring to FIG. 6, a masking film 712 a can be formed on aninner surface of the lamp cover 712 for covering and protecting the lamp710. In this case, the lamp cover 712 functions not only as a protectiondevice for the lamp 710 but also as a light reflecting plate which issimilar to the light reflecting plate 740 disposed under the light guideplate 720. The ultraviolet rays having the wavelengths of 253 nm, 313nm, 365 nm in the light emitted from the lamp 710 are firstly cut off bymeans of the masking film 703 coated on the inner surface of the glasstube 701 and then secondary broken by means of the masking film 712 acoated on the inner surface of the lamp cover 712. The masking film 712a coated on the inner surface of the lamp cover 712 can be the samematerial as that of the masking film 703 formed on the inner surface ofthe glass tube 701.

[0072] The masking film 703 can be coated on the outer surface of theglass tube 701 of the lamp 710. Hereinafter, an example of coating themasking film on the outer surface of the glass tube will be described indetail with reference to FIGS. 10, 11, 12 and 13. As shown in FIG. 10,the structure elements and the combination construction of the liquidcrystal display device are the same as those of the liquid crystaldisplay device as shown in FIG. 6, except that the masking film 703 iscoated on the outer surface of the glass tube.

[0073]FIGS. 11, 12 and 13 are a perspective view, partly broken away,and sectional views showing a construction of the lamp 710,respectively, shown in FIG. 6 in more detail.

[0074] As shown in FIGS. 11, 12 and 13, the first and second electrodes707 and 709 are disposed at both ends of the glass tube 701,respectively, in which the inert gas 711 is filled up, so as to receiveelectric signals having high and low voltages from the outside,respectively.

[0075] The first and second electrodes 707 and 709 are integrated withthe metal electrodes 707 a and 709 a, respectively, in the glass tube701. The metal electrodes 707 a and 709 a electrically discharge inresponse to the high and low voltages supplied through the first andsecond electrodes 707 and 709 thereto. The inert gas 711 that fills upthe glass tube 701 emits the ultraviolet rays 713 as the metalelectrodes 707 a and 709 a are excited due to the electric dischargethereof.

[0076] On the other hand, a fluorescent layer 705 is coated on the innersurface of the glass tube 701 to convert the part of the ultravioletrays in the light emitted from the lamp 710 into the visual rays 715,and to generate light.

[0077] In addition, the masking film 703 is coated on the outer surfaceof the glass tube 701 in order to prevent the part of the ultravioletrays 713 in the light emitted from the lamp 710 from being incidence tothe light guide plate 720.

[0078] The masking film 703 can be made of transitional metal oxide(e.g., TiO₂, Y₂O₃ or Ce₂O₅) or SiO₂. The masking film 703 is coated onthe inner surface of the glass tube 701 by a thickness of about 0.5 μmto about 1 μm. When the masking film 703 is coated on the outer surfaceof the glass tube 701 as shown in FIG. 11, the masking film 712 a may beformed on an inner surface of the lamp cover 712. The masking film 703coated on the outer surface of the glass tube 701 and the masking film712 a formed on the inner surface of the lamp cover 712 cut off theultraviolet rays which have the wavelengths of 253 nm, 313 nm and 365 nmin the light emitted from the glass tube 701. The masking film 712 acoated on the inner surface of the lamp cover 712 can be made of thesame material as that of the masking film 703 formed on the outersurface of the glass tube 701.

[0079] When the first and second electrodes 707 and 709 discharge theelectric current, the inert gas 711 is excited and generate theultraviolet rays 713. The ultraviolet rays having the wavelengths of 253nm, 313 nm and 365 nm are absorbed by the masking film 703. Accordingly,some ultraviolet rays, except for the ultraviolet rays having thewavelengths of 253 nm, 313 nm and 365 nm, and the visual rays havingwavelengths of 380 nm and 700 nm are supplied to the light guide plate720.

[0080]FIGS. 14, 15, 16 and 17 are views of showing the lamp and thebacklight assembly to which the masking films shown in FIGS. 6, 7, 8, 9,10, 11, 12 and 13 are adapted.

[0081] As shown in FIGS. 14 to 17, the first and second electrodes 707and 709 are disposed at both ends of the glass tube 701, respectively,to receive electric signals having high and low voltages from theoutside. The glass tube 701 is filled up with the inert gas 711.

[0082] The first and second electrodes 707 and 709 are integrated withthe metal electrodes 707 a and 709 a, respectively, in the glass tube701. The metal electrodes 707 a and 709 a electrically discharge inresponse to the high and low voltages supplied thereto through the firstand second electrodes 707 and 709. The inert gas 711 that fills up theglass tube 701 emits the ultraviolet rays 713 as the metal electrodes707 a and 709 a are excited by the electric discharge thereof.

[0083] On the other hand, a fluorescent layer 705 is coated on the innersurface of the glass tube 701 to convert the part of the ultravioletrays in the light emitted from the lamp 710 into the visual rays 715,thereby causing to generate light.

[0084] In addition, the masking film 703 is coated on the inner surfaceof the glass tube 701 to be placed between the fluorescent layer 705 andthe glass tube 701, and the masking film 703 a is coated on the outersurface of the glass tube 701 to cut off the part of the ultravioletrays 713 in the light emitted from the lamp 710.

[0085] The masking films 703 and 703 a are preferably made oftransitional metal oxide (e.g., TiO₂, Y₂O₃ or Ce₂O₅) or SiO₂. When themasking films 703 and 703 a are coated on inner and outer surfaces ofthe glass tube 701 as shown in FIG. 14, the masking film 712 a may befurther formed on an inner surface of the lamp cover 712. The maskingfilms 703 and 703 a coated on the inner and outer surfaces of the glasstube 701 and the masking film 712 a formed on the inner surface of thelamp cover 712 cut off the ultraviolet rays having the wavelengths of253 nm, 313 nm and 365 nm in the light emitted from the lamp 710. Themasking film 712 a coated on the inner surface of the lamp cover 712 canbe made of the same materials as those of the masking films 703 and 703a formed on the inner and outer surfaces of the glass tube 701.

[0086] When the first and second electrodes 707 and 709 discharge theelectric current, the inert gas 711 is excited and generates theultraviolet rays 713. The ultraviolet rays having the wavelengths of 253nm, 313 nm and 365 nm are absorbed by the masking films 703 and 703 aand the masking film 712 a. Accordingly, some ultraviolet rays, exceptfor the ultraviolet rays having the wavelengths of 253 nm, 313 nm and365 nm, and the visual rays having wavelengths of 380 nm and 700 nm areselectively supplied to the light guide plate 720.

[0087] The masking films 703, 703 a and 712 a cut off some of theultraviolet rays in the light emitted from the lamp 710, which causes todiscolor the light guide plate in yellow. Accordingly, the masking films703, 703 a and 712 a are not coated on the inner and outer surfaces ofthe glass tube 701 of the lamp 710. Thus, if it is possible to preventthe ultraviolet rays which causes discoloration of the light guide plate720 into yellow from being supplied to the light guide plate 720, themasking film 703 can be placed at a position in the pathway throughwhich that the light generated by the lamp 701 of the liquid crystaldisplay device is transmitted to the display unit 600, regardless of acertain position.

[0088]FIGS. 18, 19 and 20 are views of showing a construction of thelight guide plate 720, in which the masking film is coated on a lightincidence surface of the light guide plate 720 through which the lightemitted from the lamp 710 is transmitted to the light guide plate 720.

[0089] As shown in FIG. 18, the structure elements and the combinationconstruction thereof in the liquid crystal display device are the sameas those of the liquid crystal display device shown in FIG. 6, exceptfor the position of the masking film 703.

[0090]FIGS. 19 and 20 are a perspective view and a sectional view,respectively, showing the construction of the masking film 703 and thelight guide plate 720 shown in FIG. 18 in detail.

[0091] Referring to FIGS. 19 and 20, the masking film 703 is entirelycoated on the light incidence surface of the light guide plate 720,except for an upper end portion and a lower end portion of the lightincidence surface of the light guide plate 720. The lamp cover 712 forprotecting the lamp 710 is mounted on the light guide plate 720 with theedge portion of the lamp cover 712 closely making contact with the upperend portion and the lower end portion of the light guide plate 712.Thus, the light emitted from the lamp 710 passes through the maskingfilm 703 to be incident into the light guide plate 720. The masking film703 coated on the light incidence surface of the light guide plate 720is made of a transitional metal oxide ( e.g., TiO₂, Y₂O₃ or Ce₂O₅) orSiO₂. The masking film 703 is coated on the light incidence surface ofthe light guide plate 720 by a thickness of about 0.5 μm to about 1 μm.

[0092] When the electric signals having the high and low voltages areinput from the outside to the first and second electrodes 707 and 709disposed at both ends of the glass tube 701, which is filled up with theinert gas, the electric discharge takes place in the glass tube 701.When the first and second electrodes 707 and 709 discharge theelectricity, the inert gas 711 is excited and generates the ultravioletrays in the glass tube 701.

[0093] Some of the ultraviolet rays is converted into the visual rays bythe fluorescent layer 705 coated on the inner surface of the glass tube701 and emitted outwardly from the glass tube 701. The light 717including the ultraviolet rays and the visual rays, which is emittedfrom the lamp 710, passes through the masking film 703 coated on thelight incidence surface of the light guide plate 720 and approaches tothe light guide plate 720.

[0094] At that time, the ultraviolet rays having the wavelengths of 253nm, 313 nm and 365 nm are absorbed by the masking film 703. Thus, alight 719 which includes some ultraviolet rays, except for theultraviolet rays having the wavelengths of 253 nm, 313 nm and 365 nm,and the visual rays having wavelengths of 380 nm and 700 nm are onlysupplied to the light guide plate 720.

[0095] As shown in FIGS. 19 and 20, even though the masking film 703 isformed on the light incidence surface of the light guide plate 720, themasking film 712 a may be further coated on the inner surface of thelamp cover 712. The masking film 712 a coated on the inner surface ofthe lamp cover 712 can be made of the same material as that of themasking film 703 coated on the light incidence surface of the lightguide plate 720.

[0096]FIGS. 21 and 22 are graphs comparatively showing discoloration ofthe light guide plates of the conventional art and the present inventionin a lapse of the time.

[0097]FIGS. 21 and 22 are graphs respectively showing discolorationstates of types A, B and C, in which the type A is the COP light guideplate on which the masking film is not coated at all and the types B andC are the COP light guide plates on which at least one masking film iscoated in a pathway of the light. In the types B and C of the COP lightguide plates, electric current of 6 mA is applied to the lamp 710 in thetype B of the light guide plate and electric current of 8 mA is appliedto the lamp 710 in the type C of the light guide plate.

[0098] As shown in FIGS. 21 and 22, when the types A, B and C of the COPlight guide plates were aged at an ordinary temperature for 1000 hours,changes ΔX and ΔY of the discoloration in the type A of the COP lightguide plate, on which the masking film is not coated, were 0.01 and0.021, respectively, on the color coordinates. Meanwhile, changes ΔX andΔY of the discoloration in the types B and C of the COP light guideplates, on which at least one of masking film is coated are as follows.

[0099] In the type B of the COP light guide plate having the lamp towhich the electric current of 6 mA is applied, the change ΔX of thediscoloration on an X coordinate was nearly zero and the change ΔY ofthe discoloration on a Y coordinate was 0.002. In the type C of the COPlight guide plate having the lamp to which the electric current of 8 mAis applied, the changes ΔX and ΔY of the discoloration approached 0.003and 0.015, respectively, on the color coordinates. According to theaging test, even though the light guide plate 720 of the backlightassembly, on which the masking film 703 is coated to mask theultraviolet rays having particular wavelengths in the light emitted fromthe lamp 710, is used for a long time, the light guide plate is notsubjected to the discoloration.

[0100] Thus, even if the ultraviolet rays having the particularwavelengths, which cause discoloration of the light guide plate 720 intoyellow, are supplied to the light guide plate 720, it is possible toprevent the light guide plate from being discolored into yellow when thelight guide plate 720 absorbs the ultraviolet rays causing thediscoloration of the light guide plate 720. FIGS. 23 and 24 showsseveral examples of the light guide plate preventing the discolorationthereof.

[0101] When the COP light guide plate 720 is manufactured of mixture ofat least one of polyolefin resin composition and a resin for a lightguide plate, a transitional metal oxide (TiO₂, Y₂O₃ or Ce₂O₅) is addedto the mixture to make the light guide plate 720.

[0102] Furthermore, any one of2-(e⁻-hydroxy-5-methlyphenol)-benzotriazole and p-phenylene-bis(1,3-benzoxizine)-4-5 NE, which are benzene derivatives, can also beadded to the mixture substituting for the transitional metal oxides

[0103] As a result, it is possible to manufacture the light guide plate720 including isolation material 703 b for absorbing the ultravioletrays having the particular wavelengths of 253 nm, 313 nm and 365 nm, asshown in FIG. 23. The backlight assembly to which the light guide plate720 having the isolation material 703 b is adopted is shown in FIG. 24.

[0104] When the electric discharge is generated in the lamp 720, theinert gas 711 in the lamp 720 is excited and generate the ultravioletrays. Some of the ultraviolet rays are converted into the visual rays bythe fluorescent layer 705 coated on the inner surface of the glass tube701 and the visual rays are emitted from the glass tube along with theultraviolet rays. The light 717 a emitted from the lamp 710, whichinclude the ultraviolet rays and the visual rays, is incident into thelight guide plate 720 while the ultraviolet rays having the wavelengthsof 253 nm, 313 nm and 365 nm are absorbed by the isolation material 703b added to the light guide plate 720. Accordingly, only the light 719 awhich includes the ultraviolet rays, except for the ultraviolet rayshaving the wavelengths of 253 nm, 313 nm and 365 nm, and the visual rayshaving the wavelengths of 380 nm and 700 nm are supplied from the lightguide plate 720 to the display unit 600.

[0105] As shown in FIG. 24, when manufacturing the light guide plate 720by mixing the isolation material 703 b with resin, the masking film 712a can be coated on the inner surface of the lamp cover 712. The maskingfilm 712 a coated on the lamp cover 712 can be made of the same materialas the isolation material 703 b added to the light guide plate 720.

[0106]FIG. 25 is a graph of showing the discoloration of a type D of aCOP light guide plate having the isolation material 703 b added thereto,a type E of a COP light guide plate having no isolation material 703 band a type F of a PMMA light guide plate.

[0107] As shown in FIG. 25, when the types D and E of the COP lightguide plates and the type F of the PMMA light guide plate were aged atan ordinary temperature for 3300 hours, the changes ΔX and ΔY of thediscoloration in the type E of the COP light guide plate, to which theisolation material is not added, were 0.02 and 0.027, respectively, onthe color coordinates. And, the changes ΔX and ΔY of the discolorationin the type D of the PMMA light guide plate were 0.017 and 0.017,respectively, on the color coordinates. However, the changes ΔX and ΔYof the discoloration in the type D of the COP light guide plates, towhich the isolation material is added, were 0.012 and 0.012,respectively, on the color coordinates. According to the aging test,when the COP light guide plate, which is easy to be discolored by theultraviolet rays, is made of the mixture of the resin and thetransitional metal oxide or benzene derivative used as the isolationmaterial, the ultraviolet rays causing to discolor the light guide platein yellow is cut off by the isolation material so that the light guideplate is prevented from being discolored.

[0108]FIG. 26 is a graph of showing an isolation area of the ultravioletrays of a type D of a COP light guide plate having the isolationmaterial 703 b, a type E of a COP light guide plate having no isolationmaterial 703 b and a type F of a PMMA light guide plate. FIG. 27 is agraph of showing a maintenance rate of brightness of a type D of a COPlight guide plate having the isolation material 703 b, a type E of a COPlight guide plate having no isolation material 703 b and a type F of aPMMA light guide plate.

[0109] As shown in FIG. 26, the ultraviolet rays, which have thewavelengths of 253 nm, 313 nm and 365 nm and causing discoloration thelight guide plate into yellow, are cut off from the display unit 600 ina type D of a COP light guide plate having the isolation material 703 band a type F of a PMMA light guide plate. Besides, referring to FIG. 27,a maintenance rate of brightness for the type D of a COP light guideplate having the isolation material 703 b and the type F of a PMMA lightguide plate is 70% or more, on the other hand, the maintenance rate ofbrightness for the COP light guide plate is about 60%.

[0110] Although the embodiments of the masking films for masking theultraviolet rays causing discoloration of the light guide plate 720 intoyellow have been described with reference to FIGS. 6 through 27, themasking film should not be limited to the embodiments. That is, all ofthe masking film coated on the inner and outer surfaces of the glasstube 701, the masking film coated on the light incidence surface of thelight guide plate 720, the light guide plate made of the mixture of theresin and the transitional metal oxide, and the masking film coated onthe inner surface of the lamp cover 721 can be applied to an backlightassembly together.

[0111] According to the light source device, the backlight assembly andthe liquid crystal display device, at least one of the masking film thatis made of the transitional metal oxide and can cut off the ultravioletrays in the light, is placed in the pathway in that the light generatedby the lamp is supplied to the display unit for displaying images.

[0112] Accordingly, it is possible to prevent the ultraviolet rayshaving the particular wavelengths, which cause to discolor the lightguide plate made of the polyolefin resin composition, from beingsupplied to the light guide plate. Therefore, the light guide plate,which is made of the polyolefin resin composition widely used to make itlight in weight and small in size, can be prevented from discolored inyellow.

[0113] Although the preferred embodiments of the present invention havebeen described, it is understood that the present invention should notbe limited to these preferred embodiments but various changes andmodifications can be made by one skilled in the art within the spiritand scope of the present invention as hereinafter claimed.

What is claimed is:
 1. A light source device comprising: a glass tubefilled up with a gas filler, and including a mixture layer having afluorescence material therein; an electrode, disposed in the glass tube,for generating arc in response to an electric signal applied thereto;and a masking film, coated on the glass tube, for cutting off a part ofultraviolet rays emitted from the glass tube.
 2. The light source deviceas claimed in claim 1, wherein the masking film is coated on an innersurface of the glass tube, the inner surface of the glass tube beingplaced between the mixture layer having the fluorescence material andthe inner surface of the glass tube.
 3. The light source device asclaimed in claim 1, wherein the masking film is coated on an outersurface of the glass tube.
 4. The light source device as claimed inclaim 1, wherein the masking film is coated on both an outer surface ofthe glass tube and an inner surface of the glass tube, the inner surfaceof the glass tube being placed between the mixture layer having thefluorescence material and the inner surface of the glass tube.
 5. Thelight source device as claimed in claim 1, wherein the masking filmcomprises a transition metal oxide.
 6. The light source device asclaimed in claim 5, wherein the transition metal oxide is one selectedfrom the group consisting of TiO₂, Y₂O₃ and Ce₂O₅.
 7. The light sourcedevice as claimed in claim 1, wherein the masking film cuts offultraviolet rays having wavelengths of 253 nm, 313 nm and 365 nm.
 8. Alight source device as claimed in claim 1, wherein the masking film iscoated on the glass tube has a thickness range of about 0.5 μm to about1 μm.
 9. A light source device comprising: a glass tube filled up with agas filler, and including a mixture layer having a fluorescence materialtherein; an electrode, disposed in the glass tube, for generating arc inresponse to an electric signal applied thereto; and a masking film formasking a part of ultraviolet rays emitted from the glass tube, themasking film comprising a transition metal oxide and coated on an innersurface of the glass tube or an outer surface of the glass tube, whereinthe masking film coated on the inner surface of the glass tube is placedbetween the mixture layer and the inner surface of the glass tube. 10.The light source device as claimed in claim 9, wherein the transitionmetal oxide is one selected from the group consisting of TiO₂, Y₂O₃ andCe₂O₅.
 11. The light source device as claimed in claim 9, wherein themasking film cuts off ultraviolet rays having wavelengths of 253 nm, 313nm and 365 nm.
 12. The light source device as claimed in claim 1,wherein the masking film is coated on the glass tube has a thicknessrange of about 0.5 μm to about 1 μm.
 13. A backlight assemblycomprising: means for generating light in response to an electriccurrent applied to an electrode disposed in a glass tube, said glasstube being filled up with a gas filler and including a mixture layerhaving fluorescence material therein; means for guiding the light; meansfor displaying an image in response to the light transmitted from thelight guiding means; and means for masking a part of ultraviolet rays inthe light, said masking means being mounted in a pathway through whichthe light emitted by the light generating means is supplied to the imagedisplaying means.
 14. The backlight assembly as claimed in claim 13,wherein the masking means are disposed on at least one of an innersurface of the glass tube between the mixture layer and the glass tube,an outer surface of the glass tube and a light incidence surface of thelight guiding means in which the light emitted by the light generatingmeans.
 15. The backlight assembly as claimed in claim 14, wherein themasking means are coated on the glass tube has a thickness range ofabout 0.5 μm to about 1 μm.
 16. The backlight assembly as claimed inclaim 13, wherein the masking means comprise a transition metal oxide.17. The backlight assembly as claimed in claim 16, wherein thetransition metal oxide is one selected from the group consisting ofTiO₂, Y₂O₃ and Ce₂O₅.
 18. The backlight assembly as claimed in claim 13,wherein the masking means omprise SiO₂.
 19. The backlight assembly asclaimed in claim 13, wherein the masking means cut off ultraviolet rayshaving wavelengths of 253 nm, 313 nm and 365 nm.
 20. The backlightassembly as claimed in claim 13, further comprising means, having anopening opposite to the light incidence surface of the light guidingmeans, for receiving and protecting the light generating means, and themasking means being formed on an inner surface thereof.
 21. Thebacklight assembly as claimed in claim 13, wherein the light guidingmeans comprise at least one polyolefin resin composition.
 22. Thebacklight assembly as claimed in claim 21, wherein the light guidingmeans are formed by mixing the polyolefin resin with one selected fromthe group consisting of TiO₂, Y₂O₃, Ce₂O₅ and SiO₂.
 23. The backlightassembly as claimed in claim 21, wherein the light guiding means areformed by mixing the polyolefin resin with a benzene derivative.
 24. Thebacklight assembly as claimed in claim 21, wherein the benzenederivative is 2-(e⁻-hydroxy-5-methlyphenol)-benzotriazole orp-phenylene-bis (1,3-benzoxizine)-4-5 ne.
 25. A liquid crystal displaydevice comprising: a lamp unit for generating light in response to anelectric current applied to an electrode which is disposed in a glasstube, said glass tube being filled up with a glass filler and having amixture layer of a fluorescence material therein; a light guiding unitfor guiding the light; a display unit for displaying an image inresponse to the light transmitted from the light guiding means; maskingmeans for cutting off a part of ultraviolet rays in the light, themasking means being mounted in a pathway through which the light emittedby the light generating means is supplied to the image displaying means;a receiving unit for receiving the lamp unit and the light guiding unit;and a top chassis for adjusting a position of the display unit and forfixing the display unit to the receiving unit by being assembled to faceto the receiving unit.
 26. The liquid crystal display device as claimedin claim 25, wherein the masking means are disposed on at least one ofan inner surface of the glass tube between the mixture layer and theglass tube, an outer surface of the glass tube and a light incidencesurface of the light guiding unit in which the light emitted by thelight generating unit is incidence.
 27. The liquid crystal displaydevice as claimed in claim 26, wherein the masking means are coated onthe glass tube has a thickness range of about 0.5 μm to about 1 μm. 28.The liquid crystal display device as claimed in claim 25, wherein themasking means comprise a transition metal oxide.
 29. The liquid crystaldisplay device as claimed in claim 28, wherein the transition metaloxide is selected from the group consisting of TiO₂, Y₂O₃ and Ce₂O₅. 30.The liquid crystal display device as claimed in claim 25, wherein themasking means comprise SiO₂.
 31. The liquid crystal display device asclaimed in claim 25, wherein the masking means cut off ultraviolet rayshaving wavelengths of 253 nm, 313 nm and 365 nm.
 32. The liquid crystaldisplay device as claimed in claim 25, further comprising a lamp coverfor receiving and protecting the lamp unit, wherein said lamp cover hasan opening opposite to a light incidence surface of the light guidingunit, and the masking means are formed on an inner surface thereof. 33.The liquid crystal display device as claimed in claim 25, wherein thelight guiding unit comprises at least one polyolefin resin composition.34. The liquid crystal display device as claimed in claim 33, whereinthe light guiding means are formed by mixing the polyolefin resincomposition with one selected from the group consisting of TiO₂, Y₂O₃,Ce₂O₅ and SiO₂.
 35. The liquid crystal display device as claimed inclaim 25, wherein the light guiding means are formed by mixing thepolyolefin resin with a benzene derivative.
 36. The liquid crystaldisplay device as claimed in claim 35, wherein the benzene derivative is2-(e⁻-hydroxy-5-methlyphenol)-benzotriazole or p-phenylene-bis(1,3-benzoxizine)-4-5 ne.
 37. A liquid crystal display devicecomprising: a lamp unit for generating light in response to an electriccurrent applied to an electrode disposed in a glass tube, the glass tubebeing filled up with a gas filler and including a mixture layer having afluorescence material therein; a light guide for guiding the light; adisplay unit for displaying image in response to the light transmittedfrom the light guide; a mask for cutting off a part of ultraviolet raysin the light emitted by the glass tube, the mask made of a transitionmetal oxide and disposed on at least one of an inner surface of theglass tube, an outer surface of the glass tube and a light incidencesurface of the light guiding unit, the glass tube located between themixture layer and the glass tube, and the light guiding unit into whichthe light emitted by the lamp unit being incident; a receiving unit forreceiving the lamp unit and the light guiding unit; and a top chassisfor adjusting a position of the display unit and for fixing the displayunit to the receiving unit by being assembled to face to the receivingunit.
 38. The liquid crystal display device as claimed in claim 37,wherein the mask is coated on the glass tube by a thickness that rangesfrom about 0.5 μm to about 1 μm.
 39. The liquid crystal display deviceas claimed in claim 37, wherein the transition metal oxide is oneselected from the group consisting of TiO₂, Y₂O₃ and Ce₂O₅.
 40. Theliquid crystal display device as claimed in claim 37, wherein the maskcomprises SiO₂.
 41. The liquid crystal display device as claimed inclaim 37, wherein the mask cuts off ultraviolet rays having wavelengthsof 253 nm, 313 nm and 365 nm.
 42. The liquid crystal display device asclaimed in claim 37, further comprising a lamp cover for receiving andprotecting the lamp unit, wherein said lamp cover has an openingopposite to the light incidence surface of the light guiding unit, andthe mask is formed on an inner surface thereof.
 43. The liquid crystaldisplay device as claimed in claim 37, wherein the light guide comprisesat least one polyolefin resin composition.
 44. The liquid crystaldisplay device as claimed in claim 43, wherein the light guide is formedby mixing the polyolefin resin with one selected from the groupconsisting of TiO₂, Y₂O₃, Ce₂O₅ and SiO₂.
 45. The liquid crystal displaydevice as claimed in claim 37, wherein the light guide is formed bymixing the polyolefin resin with a benzene derivative.
 46. The liquidcrystal display device as claimed in claim 45, wherein the benzenederivative is 2-(e⁻-hydroxy-5-methlyphenol)-benzotriazole orp-phenylene-bis (1,3-benzoxizine)-4-5 ne.